Vehicle security systems are widely used to deter vehicle theft, prevent theft of valuables from a vehicle, deter vandalism, and to protect vehicle owners and occupants. A typical automobile security system, for example, includes a central processor or controller connected to a plurality of vehicle sensors. The sensors, for example, may detect opening of the trunk, hood, doors, windows, and also movement of the vehicle or within the vehicle. Ultrasonic and microwave motion detectors, vibration sensors, sound discriminators, differential pressure sensors, and switches may be used as sensors. In addition, radar sensors may be used to monitor the area proximate the vehicle.
The controller typically operates to give an alarm indication in the event of triggering of a vehicle sensor. The alarm indication may typically be a flashing of the lights and/or the sounding of the vehicle horn or a siren. In addition, the vehicle fuel supply and/or ignition power may be selectively disabled based upon an alarm condition.
A typical security system also includes a receiver associated with the controller that cooperates with one or more remote transmitters typically carried by the user as disclosed, for example, in U.S. Pat. No. 4,383,242 to Sassover et al. and U.S. Pat. No. 5,146,215 to Drori. The remote transmitter may be used to arm and disarm the vehicle security system or provide other remote control features from a predetermined range away from the vehicle. Also related to remote control of a vehicle function U.S. Pat. No. 5,252,966 to Lambropoulous et al. discloses a remote keyless entry system for a vehicle. The keyless entry system permits the user to remotely open the vehicle doors or open the vehicle trunk using a small handheld transmitter.
A relatively new development in the field of vehicle security relates to a transponder to be carried by the vehicle user, such as on a key ring. The transponder is uniquely coded to transmit a transponder radio signal to a transponder reader at the vehicle. Until the transponder reader receives the uniquely coded transponder radio signal, certain vehicle functions may not operate, such as vehicle starting, for example. The reader may include a transmitter for temporarily charging a capacitor in the transponder so that the transponder can then transmit its unique code. The transponder requires no batteries, is relatively small, and can be sealed to avoid damage from moisture. One such transponder is disclosed in U.S. Pat. No. 5,869,908 to Moczygemba et al.
The transponder feature means that a would-be thief can no longer break the ignition switch housing to start the vehicle. Instead possession of the properly coded transponder is required or the vehicle will not start. Some variations of the transponder technology can eliminate the need for the traditional mechanical key altogether. A number of manufacturers offer such transponder and reader systems including Texas Instruments of Dallas, Tex. under the designation TIRIS. U.S. Pat. No. 5,905,444 to Zimmer and U.S. Pat. No. 5,897,598 to Puetz disclose further developments in the vehicle transponder security area.
Unfortunately, due to the increased security provided by a transponder and a corresponding transponder reader, installation of a vehicle engine remote start system may be more complicated. When remotely starting the vehicle engine, the transponder is not close enough to the transponder reader to transmit the desired transponder radio signal. Accordingly, in an effort to bypass the transponder reader, installers have removed the transponder from the vehicle key and fastened it adjacent the transponder reader. Therefore, the transponder reader continuously receives the desired transponder radio signal from the transponder, and does not immobilize the vehicle engine. This method of installation, however, may disadvantageously decrease security.
U.S. Published Patent Application No. 2001/0000957 by Birchfield et al. attempts to address this problem, and discloses a remote start, passive anti-theft system for a vehicle having a transponder and transponder reader. The system includes an extra transponder positioned adjacent the transponder reader. The extra transponder includes a shielding coil that shields the transponder signal transmitted by the extra transponder except for when remote starting of the vehicle is desired.